I've been to Africa three times and spent over a month of hunting days afield. With that, I've taken over 20 different species while there. There are certainly different ways to do it. If you go to destinations such as South Africa and Namibia, you can purchase a package from 5-10 animals and then hunt those animals specifically. You can also pay the daily rate and pay per animal a la carte. I've done it both ways.
Speaking specifically about TZ, you choose a 10, 16, 21 or 28 day license. Each of these licenses then grants the hunter to hunt specific species. You will then pay on a per head basis dependent upon what you shoot. For example, if you want to kill a Lesser Kudu, then you can only shoot one of those on a 21/28 day license. I'll also say TZ is one of the most expensive countries to hunt when considering all of the countries in Africa, yet they do have some specific species only huntable in their country.
This would be my advice to anyone considering hunting Africa: select 4-6 animals you think you want to hunt. Then, do some research on if these species are even found in the same geographical location. Select a reputable outfitter and go have a great time!!! Additionally, always carry extra cash with you because there will be an animal, or two, that you don't think you want to hunt until the day you have a monster step out in front of you and you can't resist.
Africa is one of the most economical hunts in the world.